The present invention relates to an apparatus for recognizing floor condition of a cleaner, and more particularly to an apparatus and a method for recognizing carpets and stairs of a cleaning robot, which can determine whether the floor to be cleaned is a normal floor, a floor covered with a carpet, or stairs.
FIGS. 1A and 1B are a side view and a bottom view showing a conventional cleaner with infrared ray transmitter and receiver, respectively. As shown in the drawings, the infrared ray transmitter 4 and the infrared ray receiver 5 are mounted to the front portion of the bottom surface of a cleaner body 1 such that they are vertically spaced about 5 cm apart from the floor to be cleaned. In the drawings, the reference numeral "2" designates wheels and the reference numeral "3" designates a caster.
Referring to FIG. 2, there is shown a circuit for transmitting infrared ray in the conventional cleaner. As shown in the drawing, the circuit which is designated by the reference numeral "6" comprises an oscillating element 7 to which a resistor R21 for supplying a power from a power source Vcc, resistors R22 and R23, a condenser C21 for setting a time constant by cooperating with said resistors R22 and R23, and a transistor Q21 having a base connected with the output terminal P3 via a resistor 24 and a collector connected to a light emitting element, that is the infrared ray transmitter 4 via a resistor R25.
Referring to FIG. 3, there is shown a circuit for receiving infrared ray in the conventional cleaner. As shown in the drawing, the circuit comprises a receiving detector unit 71 which includes resistors R31 to R33, diodes D31 and D32, condensers C31 and C32 and a transistor Q31 and functions to detect the infrared ray received in the infrared ray receiver 5, that is a light receiving element, as a sine wave, a receiving amplifier unit 72 which includes resistors R34 to R40, condensers C33 to C37 and an operational amplifier OP31 and functions to compare the output signal from the infrared ray receiver 5 with an offset voltage and then amplify it, and a receiving demodulator unit 73 which includes inverters IN31 to IN33, a diode D33, a condenser C38 and a resistor R41 and functions to smooth the output signal from said receiving amplifier unit 72 to demodulate it and then apply it to the input terminal PAO of a microcomputer 73.
Operations of the above-mentioned circuits will now be described.
The oscillating element 7 of the infrared ray transmitting circuit 6 generates square wave of 1 KHz according to the time constant set by the resistors R22 and R23 and the condenser C21. The 1 KHz square wave which is outputted from the output terminal P3 of the oscillating element 7 is applied to the base of the transistor Q21 via the resistor R24 so that the transistor Q21 is turned on or off, thereby causing the infrared ray transmitter 4 to transmit infrared ray at the period of 1 msec (=1/1 KHz).
The infrared signals outputted from the infrared ray transmitter 4 as above-mentioned are reflected against the floor and then received in the infrared ray receiver 5. Accordingly, the infrared ray receiver 5 also repeats to be turned on and off at the period of 1 msec so that sine waves are outputted, at the period of 1 msec, from the output terminal of the receiving detector 71 which is connected to the collector of the infrared ray receiver 5.
On the other hand, the amount of the infrared ray signals received in the infrared ray receiver 5 varies depending on the floor condition.
For example, in the case of a normal floor shown in FIG. 4A, all infrared ray signals are directly reflected and received in the infrared ray receiver 5, so that the amount of infrared ray signals received in the infrared ray receiver 5 is greatly different from that in the case that the infrared ray receiver 5 receives no infrared ray. In the case of a carpet covered floor shown in FIG. 4B, however, a part of infrared ray signals transmitted from the infrared ray transmitter 4 are absorbed in the carpet and only the remained part of transmitted infrared ray signals are reflected against the carpet. As a result, the amount of infrared ray signals received in the infrared ray receiver 5 is slightly different from that in the case that the infrared ray receiver 5 receives no infrared ray. On the other hand, in the case of stairs or a very steep surface as shown in FIGS. 4C to 4E, infrared ray signals transmitted from the infrared ray transmitter 4 are reflected from a distant surface and then received in the infrared ray receiver 5. Accordingly, the amount of infrared ray signals received in the infrared ray receiver 5 is slightly different from that in the case that the infrared ray receiver 5 receives no infrared ray.
Depending on such difference in amounts of infrared ray signals received in the infrared ray receiver 5, the amount of current passing through the infrared ray receiver 5 varies. On the other hand, sine wave signals are outputted, at the period of 1 msec, from the output of the receiving detector unit 71 connected to the collector of the infrared ray receiver 5. The amplitude of the sine wave signals is in proportion to the difference between the amount of infrared ray signals received in the infrared ray receiver 5 is slightly and the amount of infrared ray signals in the case that the infrared ray receiver 5 receives no infrared ray. Consequently, the amplitude of sine wave signals outputted from the receiving detector unit 71 is large in the case of FIG. 4A, while it is small in the case of FIGS. 4B to 4E.
These sine wave signals outputted from the receiving detector unit 71 are applied to the inverting input terminal of the operational amplifier OP31, via the condenser C33, the resistor R39 and the condenser C35 of the receiving amplifier unit 72 and then compared with the DC offset voltage predetermined by the variable resistor R35. Thereafter, the compared sine wave signals are amplified at the rate of R38/R39 and then applied to the inverter IN31 of the receiving demodulator unit 73. At this time, if the DC offset voltage is predetermined to the voltage applied to the inverting input terminal of the operational amplifier OP31, when sine wave signals of large amplitude are outputted from the receiver detector unit 71 as in the case of FIG. 4A, low potential signals are outputted from the operational amplifier OP31. Accordingly, the inverter IN31 outputs peak signals of high potential, which is then smoothed at the condenser C38 and the resistor R41, via the diode D33. At this time, the voltages smoothed at the condenser C38 are maintained above a predetermined value, since high potential peak signals are outputted from the inverter IN31, at the period of 1 msec. This smoothed voltages are inverted into low potential signals at the inverter IN32. At the inverter IN33, the low signals are then inverted into high potential signals which is applied to the input terminal PAO of the microcomputer 8. Thus, the microcomputer 8 recognizes that the floor to be cleaned is a normal floor.
On the other hand, when sine wave signals of small amplitude is outputted from the receiving detector unit 71, as in the cases of FIGS. 4B to 4E, the operational amplifier OP31 outputs continuously high potential signals, thereby causing the inverter IN31 to output low potential signals. As a result, low level signals are applied to the input terminal PAO of the microcomputer 8, so that the microcomputer 8 recognizes that the floor to be cleaned is not a normal floor, but a carpet covered floor.
Although the above-mentioned conventional circuit can determine a normal floor and a carpet covered floor, it may mistake stairs or a very steep surface for the carpet covered floor. As a result, there is a disadvantage of providing no protection of cleaning robots from stairs or a very steep surface.
In addition, external light beams may cause malfunction of the circuit in discriminating between a normal floor and a carpet covered floor.